Microwave antenna

ABSTRACT

According to one aspect of the present disclosure, a microwave antenna assembly is disclosed. The antenna assembly includes a feedline having an inner conductor, an outer conductor and an inner insulator disposed therebetween and a radiating portion including a dipole antenna having a proximal portion and a distal portion. The antenna assembly also comprises a sheath disposed over the feedline and the radiating portion defining a chamber around the feedline and the radiating portion. The chamber is adapted to circulate coolant fluid therethrough. The antenna assembly further includes a connection hub having cable connector coupled to the feedline, an inlet fluid port and an outlet fluid port. The connection hub includes a bypass tube configured to provide for flow of the coolant fluid from the cable connector directly to the outlet fluid port.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/925,025, filed on Oct. 28, 2015, which is acontinuation of application U.S. patent application Ser. No. 14/659,860,filed on Mar. 17, 2015, now U.S. Pat. No. 9,198,725, which is acontinuation application of U.S. patent application Ser. No. 14/338,509,filed Jul. 23, 2014, now U.S. Pat. No. 9,113,932, which is acontinuation application of U.S. patent application Ser. No. 14/014,937,filed Aug. 30, 2013, now U.S. Pat. No. 8,795,268, which is acontinuation application of U.S. patent application Ser. No. 13/596,785,filed Aug. 28, 2012, now U.S. Pat. No. 8,523,854, which is acontinuation application of U.S. patent application Ser. No. 12/199,935,filed Aug. 28, 2008, now U.S. Pat. No. 8,251,987, the entire contentseach of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave antennas used intissue ablation procedures. More particularly, the present disclosure isdirected to a microwave antenna having a coolant assembly forcirculating a dielectric coolant fluid through the microwave antenna.

2. Background of Related Art

Treatment of certain diseases requires destruction of malignant tissuegrowths (e.g., tumors). It is known that tumor cells denature atelevated temperatures that are slightly lower than temperaturesinjurious to surrounding healthy cells. Therefore, known treatmentmethods, such as hyperthermia therapy, heat tumor cells to temperaturesabove 41° C., while maintaining adjacent healthy cells at lowertemperatures to avoid irreversible cell damage. Such methods involveapplying electromagnetic radiation to heat tissue and include ablationand coagulation of tissue. In particular, microwave energy is used tocoagulate and/or ablate tissue to denature or kill the cancerous cells.

Microwave energy is applied via microwave ablation antennas thatpenetrate tissue to reach tumors. There are several types of microwaveantennas, such as monopole and dipole, in which microwave energyradiates perpendicularly from the axis of the conductor. A monopoleantenna includes a single, elongated microwave conductor whereas adipole antenna includes two conductors. In a dipole antenna, theconductors may be in a coaxial configuration including an innerconductor and an outer conductor separated by a dielectric portion. Morespecifically, dipole microwave antennas may have a long, thin innerconductor that extends along a longitudinal axis of the antenna and issurrounded by an outer conductor. In certain variations, a portion orportions of the outer conductor may be selectively removed to providemore effective outward radiation of energy. This type of microwaveantenna construction is typically referred to as a “leaky waveguide” or“leaky coaxial” antenna.

Conventional microwave antennas have a narrow operational bandwidth, awavelength range at which optimal operational efficiency is achieved,and hence, are incapable of maintaining a predetermined impedance matchbetween the microwave delivery system (e.g., generator, cable, etc.) andthe tissue surrounding the microwave antenna. More specifically, asmicrowave energy is applied to tissue, the dielectric constant of thetissue immediately surrounding the microwave antenna decreases as thetissue is cooked. The drop causes the wavelength of the microwave energybeing applied to tissue to increase beyond the bandwidth of the antenna.As a result, there is a mismatch between the bandwidth of conventionalmicrowave antenna and the microwave energy being applied. Thus, narrowband microwave antennas may detune hindering effective energy deliveryand dispersion.

SUMMARY

According to one aspect of the present disclosure, a microwave antennaassembly is disclosed. The antenna assembly includes a feedline havingan inner conductor, an outer conductor and an inner insulator disposedtherebetween and a radiating portion including a dipole antenna having aproximal portion and a distal portion. The antenna assembly alsocomprises a sheath disposed over the feedline and the radiating portiondefining a chamber around the feedline and the radiating portion. Thechamber is adapted to circulate coolant fluid therethrough. The antennaassembly further includes a connection hub having cable connectorcoupled to the feedline, an inlet fluid port and an outlet fluid port.The connection hub includes a bypass tube configured to provide for flowof the coolant fluid from the cable connector directly to the outletfluid port.

According another aspect of the present disclosure, a microwave antennaassembly is disclosed. The antenna assembly includes a feedline havingan inner conductor, an outer conductor and an inner insulator disposedtherebetween and a radiating portion including a dipole antenna having aproximal portion and a distal portion. The antenna assembly alsocomprises a sheath disposed over the feedline and the radiating portiondefining a chamber around the feedline and the radiating portion. Thechamber is adapted to circulate coolant fluid therethrough. The antennaassembly further includes a three-branch connection hub including afirst branch having a cable connector coupled to the feedline at ajunction point, a second branch having an outlet port, a third branchhaving an inlet port, and a bypass tube in fluid communication with aproximal end of the first branch and the outlet port, wherein one end ofthe bypass tube is in proximity with the junction point to provide forflow of the coolant fluid therethrough.

A method for manufacturing a microwave antenna assembly is alsocontemplated by the present disclosure. The antenna assembly includes afeedline including an inner conductor, an outer conductor and an innerinsulator disposed therebetween and a radiating portion including adipole antenna having a proximal portion and a distal portion. Themethod includes the step of enclosing the feedline and the radiatingportion in a sheath to define a chamber around the feedline and theradiating portion. The chamber is adapted to circulate coolant fluidtherethrough. The method also includes the step of coupling athree-branch connection hub to the feedline and the sheath. Thethree-branch connection hub including a first branch having a cableconnector coupled to the feedline at a junction point, a second branchhaving an outlet port, a third branch having an inlet port. A step ofinterconnecting a proximal end of the first branch and the outlet portvia a bypass tube is also provided by the method. One end of the bypasstube is in proximity with the junction point to provide for flow of thecoolant fluid therethrough

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram of the microwave ablation system accordingto an embodiment of the present disclosure;

FIG. 2 is a perspective, internal view of the microwave antenna assemblyaccording to the present disclosure;

FIGS. 3 and 4 are enlarged, cross-sectional views of a portion of themicrowave antenna assembly of FIG. 1;

FIG. 5 is a side view of an interchangeable tip (or a sheath and a tipassembly) for use with the microwave antenna assembly of FIG. 1;

FIG. 6 is a schematic, top view of a connection hub of the microwaveantenna assembly of FIG. 1 according to the present disclosure;

FIG. 7 a cross-sectional view of a series of inflow tubes of themicrowave antenna assembly of FIG. 1 according to the presentdisclosure;

FIG. 8 is a topside view of a proximal portion of the microwave antennaassembly of FIG. 1 according to the present disclosure;

FIG. 9 is a side view of a proximal end of the feedline of the microwaveantenna assembly of FIG. 1 according to the present disclosure;

FIG. 10 is a side view of a cable connector of the microwave antennaassembly of FIG. 1 according to the present disclosure;

FIG. 11 is a top view of a connection hub of the microwave antennaassembly of FIG. 1 according to the present disclosure;

FIGS. 12A and B are perspective and side views of the connection hub ofthe microwave antenna assembly of FIG. 1 according to the presentdisclosure;

FIG. 13 is a top view of a connection hub of the microwave antennaassembly of FIG. 1 with parts disassembled according to the presentdisclosure;

FIG. 14 is a top view of a connection hub of the microwave antennaassembly of FIG. 1 according to one embodiment of the presentdisclosure; and

FIG. 15 is a top view of a connection hub of the microwave antennaassembly of FIG. 1 with parts disassembled according to one embodimentof the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure will be describedherein below with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail.

FIG. 1 shows a microwave ablation system 10 that includes a microwaveantenna assembly 12 coupled to a microwave generator 14 via a flexiblecoaxial cable 16. The generator 14 is configured to provide microwaveenergy at an operational frequency from about 500 MHz to about 5000 MHzalthough other suitable frequencies are also contemplated.

The antenna assembly 12 includes a radiating portion 18 connected byfeedline 20 (or shaft) to the cable 16. More specifically, the antennaassembly 12 is coupled to the cable 16 through a connection hub 22having an outlet fluid port 30 and an inlet fluid port 32 that areconnected in fluid communication with a sheath 38. The sheath 38encloses radiating portion 18 and feedline 20 allowing a coolant fluid37 to circulate from ports 30 and 32 around the antenna assembly 12. Theports 30 and 32 are also coupled to a supply pump 34 that is, in turn,coupled to a supply tank 36 via supply line 86. The supply pump 34 maybe a peristaltic pump or any other suitable type. The supply tank 36stores the coolant fluid 37 and in one embodiment, may maintain thefluid at a predetermined temperature. More specifically, the supply tank36 may include a coolant unit that cools the returning liquid from theantenna assembly 12. In another embodiment, the coolant fluid 37 may bea gas and/or a mixture of fluid and gas.

FIG. 2 illustrates the radiating portion 18 of the antenna assembly 12having a dipole antenna 40. The dipole antenna 40 is coupled to thefeedline 20 that electrically connects antenna assembly 12 to thegenerator 14. As shown in FIG. 3-4, the feedline 20 includes an innerconductor 50 (e.g., wire) surrounded by an inner insulator 52, which issurrounded by an outer conductor 56 (e.g., cylindrical conductingsheath). The inner and outer conductors 50 and 56 respectively, may beconstructed of copper, gold, stainless steel or other conductive metalswith similar conductivity values. The metals may be plated with othermaterials, e.g., other conductive materials, to improve theirproperties, e.g., to improve conductivity or decrease energy loss, etc.In one embodiment, the feedline 20 may be formed from a coaxialsemi-rigid or flexible cable having a wire with a 0.047″ outer diameterrated for 50 Ohms.

The dipole antenna 40 includes a proximal portion 42 and a distalportion 44 interconnected at a feed point 46. The distal portion 44 andthe proximal portion 42 may be either balanced (e.g., of equal lengths)or unbalanced (e.g., of unequal lengths). The proximal portion 42 isformed from the inner conductor 50 and the inner insulator 52 which areextended outside the outer conductor 56, as shown best in FIG. 4. In oneembodiment, in which the feedline 20 is formed from a coaxial cable, theouter conductor 56 and the inner insulator 52 may be stripped to revealthe inner conductor 50, as shown in FIG. 3.

FIG. 3 illustrates the distal portion 44 attached to the proximalportion 42. The distal portion 44 may be soldered to the inner conductor50 of the proximal portion 42 to establish electromechanical contacttherebetween. A portion of the distal end of the inner conductor 50 isinserted into the distal portion 44 such that a dipole feed gap “G”remains between the proximal and distal portions 42 and 44 at the feedpoint 46. The gap “G” may be from about 1 mm to about 3 mm. In oneembodiment, the gap “G” may be thereafter filled with a dielectricmaterial at the feed point 46. In another embodiment, the innerinsulator 52 is extended into the feed point 46. The dielectric materialmay be polytetrafluoroethylene (PTFE), such as Teflon® sold by DuPont ofWillmington, Del. In another embodiment, as shown in FIG. 3, the gap “G”may be coated with a dielectric seal coating as discussed in more detailbelow.

With reference to FIGS. 2 and 4, the antenna assembly 12 also includes achoke 60. The choke 60 is disposed around the feedline 20 and includesan inner dielectric layer 62 and an outer conductive layer 64. The choke60 may be a quarter-wavelength shorted choke and is shorted to the outerconductor 56 of the feedline 20 at the proximal end (not illustrated) ofthe choke 60 by soldering or other suitable methods. In one embodiment,the dielectric layer 62 is formed from a fluoropolymer, such astetrafluorethylene, perfluorpropylene, and the like, and has a thicknessof about 0.005 inches. The dielectric of dielectric layer 62 may extendpast the choke conductor layer 64 toward the distal end of the assembly12, as shown in FIG. 2.

Since the radiating portion 18 and the feedline 20 are in direct contactwith the coolant fluid 37 these components of the assembly 12 are sealedby a protective sleeve 63 (FIG. 3) to prevent any fluid seeping therein.This may be accomplished by applying any type of melt-processiblepolymers using conventional injection molding and screw extrusiontechniques. In one embodiment, a sleeve of fluorinated ethylenepropylene (FEP) shrink wrap may be applied to the entire assembly 12,namely the feedline 20 and the radiating portion 18, as shown in FIGS. 3and 4. The protective sleeve 63 is then heated to seal the feedline 20and radiating portion 18. The protective sleeve 63 prevents any coolantfluid 37 from penetrating into the assembly 12. The protective sleeve 63may be applied either prior to or after applying the outer conductivelayer 64. In addition, protective sleeve 63 may also be applied at thepoint where the inner conductor 50 and the inner insulator 52 areextended past the outer conductor 56, thereby creating a vacuum 53 asshown in FIG. 3.

Assembly 12 also includes a tip 48 having a tapered end 24 thatterminates, in one embodiment, at a pointed end 26 to allow forinsertion into tissue with minimal resistance at a distal end of theradiating portion 18. In those cases where the radiating portion 18 isinserted into a pre-existing opening, tip 48 may be rounded or flat.

The tip 48, which may be formed from a variety of heat-resistantmaterials suitable for penetrating tissue, such as metals (e.g.,stainless steel) and various thermoplastic materials, such aspoletherimide, polyamide thermoplastic resins, an example of which isUItem® sold by General Electric Co. of Fairfield, Conn. The tip 48 maybe machined from various stock rods to obtain a desired shape. The tip48 may be attached to the distal portion 44 using various adhesives,such as epoxy seal. If the tip 48 is metal, the tip 48 may be solderedto the distal portion 44.

FIG. 5 illustrates various shapes and forms of the tip 48, namely astainless steel tip 48 a and a dielectric tip 48 b. Both tips 48 a and48 b include an insertion base 51 having an external diameter that issmaller than diameter of the tips 48 a and 48 b allowing for easierinsertion into the sheath 38. This configuration also provides for abetter seal between the tip 48 and the sheath 38. The sheath 38 enclosesthe feedline 20, the radiating portion 18 from the tip 48 to the base 81(FIG. 6). The sheath 38 is also secured to the base 81 of the connectionhub 22 and the tip 48 such that the sheath 38 is in fluid communicationwith the connection hub 22 and defines a chamber 89 (FIG. 3) between thebase 81 and the tip 48. The coolant fluid 37 is supplied by the pump 34and is circulated in the chamber 89 between the radiating portion 18,the feedline 20 and the sheath 38. The sheath 38 may be any type ofrigid tube, such as a catheter manufactured from polyimide and othertypes of polymers. The sheath 38 may be assembled by initially securingthe tip 48 to the distal end of the sheath 38 and then inserting thecombined sheath and tip assembly onto the assembly 12.

The assembly 12 also includes the connection hub 22, as shown in moredetail in FIG. 6. The connection hub 22 includes a cable connector 79and fluid ports 30 and 32. The connection hub 22 may include athree-branch luer type connector 72, with a first branch 74 being usedto house the cable connector 79 and the second and third branches 76 and78 to house the outlet and inlet fluid ports 30 and 32, respectively. Inone embodiment, the connection hub 22 may include only the first branch74 or two of the branches 74, 76, 78 and have the fluid ports 30 and 32disposed directly on the first branch 74.

The connection hub 22 also includes a base 81 disposed at a distal endof the first branch 74. More than one inflow 86 and outflow 88 tube maybe used. The outflow tube 88 is coupled to the second branch 76 and isin fluid communication with the bypass tube 80 through the second branch76. In one embodiment, the assembly 12 includes one or more inflow tubes86 a and 86 b that are fed through the third branch 78 as shown in FIG.6.

In one embodiment, the second and third branches 76 and 78 may includevarious types of female and/or male luer connectors adapted to coupleinflow and outflow tubes 86 and 88, respectively, from the pump 34 tothe assembly 12. FIG. 7 shows the assembly 12 including two inflow tubes86 a and 86 b. The inflow tubes 86 a and 86 b may be any type offlexible tube having an external diameter sufficient to fit inside achamber 89 between the feedline 20 and the sheath 38. The inflow tubes86 a and 86 b are inserted through the inlet fluid port 32. Morespecifically, as illustrated in FIG. 8, a female connector 102 may becoupled to the inlet port 32 either directly or to an intermediate maleluer connector 104. The distal ends of the tubes 86 a and 86 b areinserted through an internal support member 103 of the female connector102, which secures the tubes 86 a and 86 b thereto. The female and maleconnectors 102 and 104 allow for easy coupling of the assembly 12 to thecoolant fluid system. The inflow tubes 86 a and 86 b may be secured tothe third branch 78 via a glue plug 105, which may be formed by flowingglue into the third branch 78 and curing the glue via an ultravioletsource or other way known in the art.

The inflow tube 86 a is inserted into the distal end of the distalportion 44 and the inflow tube 86 b is inserted at a point proximate themidpoint of the assembly 12 (e.g., the feed point 46), as shown in FIG.7. The inflow tubes 86 a and 86 b are then secured to the radiatingportion 18 (e.g., using epoxy, glue, etc.). The inflow tubes 86 a and 86b are positioned in this configuration to provide optimal coolant flowthrough the sheath 38. The fluid flow from the inflow tube 86 a isdirected into the tip 48 and reflected in the proximal direction. Thefluid flow from the inflow tube 86 b provides the coolant fluid 37 alongthe radiating portion 18. During operation, the pump 34 supplies fluidto the assembly 12 through the inflow tubes 86 a and 86 b, therebycirculating the coolant fluid 37 through the entire length of theassembly 12 including the connection hub 22. The coolant fluid 37 isthen withdrawn from the first branch 74 and the second branch 76 throughthe outlet fluid port 30.

The above-discussed coolant system provides for circulation ofdielectric coolant fluid 37 (e.g., saline, deionized water, etc.)through the entire length of the antenna assembly 12. The dielectriccoolant fluid 37 removes the heat generated by the assembly 12. Inaddition, the dielectric coolant fluid 37 acts as a buffer for theassembly 12 and prevents near field dielectric properties of theassembly 12 from changing due to varying tissue dielectric properties.For example, as microwave energy is applied during ablation, desiccationof the tissue around the radiating portion 18 results in a drop intissue complex permittivity by a considerable factor (e.g., about 10times). The dielectric constant (er′) drop increases the wavelength ofmicrowave energy in the tissue, which affects the impedance ofun-buffered microwave antenna assemblies, thereby mismatching theantenna assemblies from the system impedance (e.g., impedance of thecable 16 and the generator 14). The increase in wavelength also resultsin a power dissipation zone which is much longer in length along theassembly 12 than in cross sectional diameter. The decrease in tissueconductivity (er″) also affects the real part of the impedance of theassembly 12. The fluid dielectric buffering according to the presentdisclosure also moderates the increase in wavelength of the deliveredenergy and drop in conductivity of the near field, thereby reducing thechange in impedance of the assembly 12, allowing for a more consistentantenna-to-system impedance match and spherical power dissipation zonedespite tissue behavior.

Referring to FIGS. 9 and 10, the cable connector 79 is coupled to theinner conductor 50 and outer conductor 56. More specifically, the innerconductor 50 and the inner insulator 52 extend outside the outerconductor 56 at the proximal end of the feedline 20 and the cableconnector 79 is coupled to the inner and outer conductors 50 and 56. Thecable connector 79 may be any type of threaded or snap connector adaptedto contact the outer conductor 56 and the inner conductor 50. In oneembodiment, the cable connector 79 may be an SMA type connector havingan outer conductor 91, an insulator (not explicitly shown), and an innerconductor 92, which may be a hollow pin. The inner conductor 92 of thecable connector 79 fits about the inner conductor 50 and the outerconductor 91 thereof contacts the outer conductor 56, with the insulatorspacing the outer and inner conductors 91 and 92 apart. Cable connector79 may be secured to the inner and outer conductors 50 and 56 usingsoldering, laser welding and other suitable ways, which provideelectromechanical contact therebetween at a junction point 93.

Laser welding allows coupling the cable connector 79 to the feedline 20.However, care must be exercised to avoid damaging the outer conductor 56by the laser. Soldering avoids this issue, but at higher power levels(e.g., about 90 or more Watts) the soldering connection may begin toreflow due to the excessive heat generated by increased power.Embodiments of the present disclosure also provide for a system andmethod to alleviate the solder reflow by circulating a dielectriccoolant fluid through the entire length of the assembly 12 up to thecable connector 79 such that the junction point 93 of the connector 79to the inner and outer conductors 50 and 56 is cooled.

The connector 79 includes a threaded portion 94 that couples to thedistal end of the cable 16, which may also have a corresponding SMA maleconnector. The connection hub 22 is inserted onto the distal end of thefeedline 20 and is slid toward the distal end thereof. The cableconnector 79 is then coupled to the proximal end of the first branch 74thereby securing the connector hub 22 to the feedline 20 (e.g., gluingthe connector hub 22 to the cable connector 79).

FIGS. 11 and 12 illustrate one embodiment wherein the first and secondbranches 74 and 76 are interconnected via a bypass tube 80. A beveledopening 82 is formed in the wall of the second branch 76 and is angledtoward the outlet fluid port 30, as shown in FIG. 11.

This configuration provides easier insertion of the bypass tube 80 intothe second branch 76 as shown in FIGS. 12A-B and 13. An outlet opening84 is also formed in the first branch 74, at approximately the proximalend thereof such that the outlet opening 84 is proximate the junctionpoint 93 of the connector 79 and the feedline 20 allowing the coolantfluid 37 to contact the connector 79. The outlet opening 84 may beformed at any angle suitable for providing fluid flow between the firstbranch 74 and the second branch 76. A first end of the bypass tube 80 isattached to the outlet opening 84 such that the first end of the bypasstube 80 is proximate to the junction point 93. A second end of thebypass tube 80 is thereafter inserted through the second branch 76 andthe outlet port 30 and is coupled to a male luer type connector 100,which provides for quick coupling and decoupling to the outflow tube 88,as shown in FIG. 13. The bypass tube 80 may be attached to the openings82 and 84 using a variety of adhesives and other means suitable forsealing any gaps between the openings 82 and 84 and the bypass tube 80.The bypass tube 80 may be compression fit into the male connector 100and/or glued thereto. The outlet port 30 is sealed via a glue plug orother means around the bypass tube 80, thereby limiting the coolantfluid 37 to outflow through the bypass tube 80. This configurationallows the coolant fluid to flow from the assembly 12 only through theopening 84.

In conventional designs, vapor pockets form at the junction between theconnector 79 and the feedline 20 and prevent the coolant fluid 37 fromreaching the connector 79, thereby preventing any cooling to take place.As a result, the connector 79 continues to heat up and solder attachingthe coupling the connector 79 melts. The bypass tube 80 provides forunrestricted flow of the coolant fluid from the proximal end of thefirst branch 74 and the connector 79. The bypass tube 80 provides forflow of the coolant fluid directly from the cable connector 79 to theoutlet port 30 without withdrawing fluid through the second branch 76.This configuration removes the fluid from the assembly 12 at a ratesufficient to prevent vaporization of the fluid as it comes in contactwith the junction point 93 of the connector 79, thereby preventingformation of vapor pockets. In other words, the bypass tube 80 allowsfor the coolant fluid to circuit to the connector 79 withoutrestrictions caused by pressure build-up resulting from the heatgenerated at the junction point 93.

The above-discussed coolant system provides circulation of dielectriccoolant fluid 37 (e.g., saline, deionized water, etc.) through theentire length of the antenna assembly 12. In addition, the coolant isalso brought in contact with the cable connector 79 allowing use of aconventional solder connection to attach the connector 79 to thefeedline 20. The fluid provides cooling and enhances dielectric matchingproperties of the assembly 12. The coolant fluid 37 supplied to thecable connector 79 prevents solder re-flow, allowing the assembly 12 tooperate at higher power levels (e.g., 150 watts). The coolant fluid 37circulated through the sheath 38 also wicks heat away from the feedline20, which allows delivery of high power signals to the antenna radiatingsection.

FIGS. 14 and 15 illustrate another embodiment of the connection hub 22having a bifurcated outflow path configuration, in which the secondbranch 76 also acts as an outflow path. The connection hub 22 as shownin FIG. 14 does not include the beveled opening 82 since the bypass tube80 is coupled to the opening 84 within the first branch 74 and is feddirectly into a bifurcated coupler 106. The bifurcated coupler 106includes a male luer connector 108 at a proximal end thereof and abifurcated port 110 at a distal end thereof. The bifurcated port 110includes a first port 112 and a second port 114 which are separated by amember 113 at the distal end of the bifurcated port 110 such that thefirst and second ports 112 and 114 then meet at a chamber 115. The firstport 112 is coupled to the second branch 76 through the connector 100and the second port 114 is coupled to bypass tube 80. This configurationprovides for a dual outflow of the coolant fluid 37, from the secondbranch 76 and the bypass tube 80 and allows for an increased flow ratethrough the assembly 12.

The described embodiments of the present disclosure are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present disclosure. Embodiments of the presentdisclosure may also be implemented in a microwave monopolar antenna orother electrosurgical devices. Various modifications and variations canbe made without departing from the spirit or scope of the disclosure asset forth in the following claims both literally and in equivalentsrecognized in law.

1-18. (canceled)
 19. A microwave antenna assembly comprising: a hubincluding a proximal portion and a distal portion; a sheath extendingdistally from the hub, the sheath defining a chamber; a feedlineconfigured to deliver microwave energy, the feedline including an innerconductor, an outer conductor, and an inner insulator disposed betweenat least a portion of the inner conductor and the outer conductor,wherein at least a portion of the feedline is disposed within thechamber defined by the sheath; and a fluid flow tube disposed within thechamber defined by the sheath, the fluid flow tube configured to delivera fluid to the chamber defined by the sheath to cool the portion of thefeedline disposed within the chamber defined by the sheath and to coolthe proximal portion of the hub.
 20. The microwave antenna assemblyaccording to claim 19, wherein the fluid is a gas, a liquid, or acombination of a gas and a liquid.
 21. The microwave antenna assemblyaccording to claim 19, further comprising: a dielectric layer formedcircumferentially about at least a portion of the outer conductor; and aconductive layer formed circumferentially about at least a portion ofthe dielectric layer, at least a portion of the conductive layerelectrically coupled to a portion of the outer conductor of thefeedline, wherein the dielectric layer and the conductive layer limitpropagation of microwave energy in a proximal direction.
 22. Themicrowave antenna assembly according to claim 21, wherein the conductivelayer includes a proximal end electrically coupled to the outerconductor of the feedline.
 23. The microwave antenna assembly accordingto claim 21, wherein the dielectric layer and the conductive layerdefine a quarter wavelength choke.
 24. The microwave antenna assemblyaccording to claim 21, further comprising a second dielectric layerformed circumferentially about the dielectric layer between thedielectric layer and the conductive layer.
 25. The microwave antennaassembly according to claim 21, wherein the feedline includes aradiating potion configured to deliver microwave energy to tissue and adistal end of the conductive layer is disposed proximal a proximal endof the radiating portion.
 26. The microwave antenna assembly accordingto claim 19, wherein the fluid flow tube extends through the hub andinto the chamber defined by the sheath.
 27. The microwave antennaassembly according to claim 19, wherein the fluid flow tube is disposedadjacent at least a portion of the feedline within the chamber definedby the sheath.
 28. The microwave antenna assembly according to claim 19,wherein the feedline includes a radiating portion configured to delivermicrowave energy to tissue and wherein a distal end of the fluid flowtube is disposed proximal to the radiating portion.
 29. The microwaveantenna assembly according to claim 19, further comprising a tipdisposed at a distal portion of the microwave antenna assembly, whereinfluid flow from the fluid inflow tube is directed in a direction of thetip and reflected in a proximal direction.
 30. The microwave antennaassembly according to claim 19, further comprising a second fluid flowtube configured to deliver fluid, a distal end of the second flow tubedisposed distal a distal end of the fluid flow tube.
 31. A systemcomprising: a microwave generator; a fluid supply; and a microwaveantenna assembly configured to couple to the microwave generator and thefluid supply, the microwave antenna assembly comprising: a hub includinga proximal portion and a distal portion; a sheath extending distallyfrom the hub, the sheath defining a chamber; a feedline configured todeliver microwave energy generated by the microwave generator, thefeedline including an inner conductor, an outer conductor, and an innerinsulator disposed between at least a portion of the inner conductor andthe outer conductor, wherein at least a portion of the feedline isdisposed within the chamber defined by the sheath; and a fluid flow tubedisposed within the chamber defined by the sheath, the fluid flow tubeconfigured to deliver a fluid from the fluid supply to the chamberdefined by the sheath to cool the portion of the feedline disposedwithin the chamber defined by the sheath and to cool the proximalportion of the hub.
 32. The system according to claim 32, wherein thefluid is a gas, a liquid or a combination of a gas and a liquid.
 33. Thesystem according to claim 31, wherein the microwave antenna assemblyincludes: a dielectric layer formed circumferentially about at least aportion of the outer conductor; and a conductive layer formedcircumferentially about at least a portion of the dielectric layer, atleast a portion of the conductive layer electrically coupled to aportion of the outer conductor of the feedline, wherein the dielectriclayer and the conductive layer limit propagation of microwave energy ina proximal direction.
 34. The system according to claim 33, wherein theconductive layer includes a proximal end electrically coupled to theouter conductor of the feedline.
 35. The system according to claim 33,wherein the dielectric layer and the conductive layer define a quarterwavelength choke.
 36. The system according to claim 33, wherein themicrowave antenna assembly includes a second dielectric layer formedcircumferentially about the dielectric layer between the dielectriclayer and the conductive layer.
 37. The system according to claim 31,wherein the feedline includes a radiating portion configured to delivermicrowave energy to tissue and a distal end of the conductive layer isdisposed proximal a proximal end of the radiating portion.